The present invention relates to a method of on-line controlling tire manufacturing components.
More specifically, the present invention relates to a method of on-line controlling the quality, dimensions and structure of green road vehicle tire components.
In the road vehicle tire manufacturing industry, green components are first produced in forming devices and then processed and assembled into tires, which are then cured in respective molds.
To ensure conformance of the tires to given specifications, the green components from the forming devices are normally on-line quality controlled to ensure the respective mixes are as required, i.e. are such as to impart the required physical characteristics to the components. As it is processed and fed to the tire assembly machine, each component normally also undergoes various other on-line controls: identification control to identify and ensure the component being supplied is the one actually required; quality control to ensure given physical characteristics (elasticity, hardness, etc.) of the component; dimensional control to ensure the shape and dimensions of the component and/or the shape, dimensions and location of part of the component are as required; and structural control to ensure a given distribution of material within the component (no porosity, etc.).
On known tire manufacturing lines, all these controls are performed using various types of equipment normally comprising laser beam devices (such as the one described in U.S. Pat. No. 5537207) and optical and continuous weighing devices, all of which are capable of controlling dimensional characteristics, but not material quality.
It is an object of the present invention to provide a method of on-line controlling tire manufacturing components, designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a method of on-line controlling tire manufacturing components, whereby at least two distinct points of a said component are placed in contact with respective terminals having different electric potentials to generate an electric current between said two points; said electric current being measured to determine the value of an electric resistance of said component between said two points; and said electric resistance value being compared with at least one reference value.
When the two points, for example, are located a given distance apart, it is possible to determine the electric resistance value of the material of which the component is made, and, by comparing this value with a number of reference values (specific to the material), to determine the type of component and the percentages and dispersion of carbon black and carbon aggregates within the material.
When controlling, for example, a component, the specific electric resistance of the material of which is known by being determined beforehand using the above method, it is possible, by determining, again using the above method, the electric resistance between two given points on the component, and comparing the resistance value with a number of reference values, to determine fairly accurately the distance between the two contact points (thus enabling dimensional control of the component) and also the presence of any air pockets and/or porosity between the two points and within the component.
Finally, when the component being checked contains, for example, portions with specific characteristics, e.g. highly electrically conductive portions for grounding static, determining the electric resistance between specific points on the component provides for determining the presence or absence and the extension of the portion in question.
In each case, given a specific tolerance range about each reference value, comparing the measured resistance value with the reference value or values therefore provides for determining acceptance or rejection of the component, and whether any intervention is required on the production line.
In other words, the above method provides for performing a sort of tire production line check-up by means of controls which may be all or for the most part resistive, i.e. mostly of the same type, and wherein all the controls of the same type may possibly be performed using one control device.
The present invention also relates to a device for on-line controlling tire manufacturing components.
According to the present invention, there is provided a device for on-line controlling tire manufacturing components, the device comprising at least two terminals which are placed in contact with respective distinct points of a said component; an electric circuit connecting said terminals to each other; a voltage source located along said circuit to maintain said two terminals at different electric potentials; current-measuring means located along said circuit to determine the value of an electric resistance of said component between said points; and comparing means connected to said current-measuring means to compare said electric resistance value with at least one reference value.